Oysters (clams) have the ability to group together and stick to other oysters or a solid substrate. They create reefs that are habitats for other animal species. They protect the coasts against erosion and against waves, absorbing their force (the possibility of reducing the energy of a large wave by up to 93%). Artificial reefs are much better suited to southern waters than to northern shores. Behind the oyster reef line there are calm waters where seagrass can grow and salt marshes can form.
It is currently estimated that 85% of the world’s natural oyster reefs have been lost.
Old shells are used for reintroduction, to which young individuals attach themselves. In addition to protective measures, artificial oyster reefs are an important component of the economic reconstruction strategy of local communities, as the reefs become a source of work and food.
Example:
An interesting example of a theoretical approach to the reconstruction of oyster reefs is presented by the American landscape architect Kate Orff, who proposes to establish reefs in New York, they would play a protective role (counteract the negative effects of climate change), environmental (water purification), economic (food production) and social (creating new recreational and educational areas).
More at the link:
https://www.ted.com/talks/kate_orff_reviving_new_york_s_rivers_with_oysters
References and additional materials:
http://nrcsolutions.org/oyster-reefs/
https://www.conservationgateway.org/ConservationPractices/Marine/Documents/Shellfish%20Reefs%20at%20Risk-06.18.09-Pages.pdf